The goals of the proposed research are to determine the mechanisms that lead to the development of necrotizing enterocolitis (NEC), and to determine novel therapeutic strategies for this devastating disease. To do so, we will explore novel roles of the Aryl Hydrocarbon Receptor (AHR) in the pathogenesis of NEC through its previously unrecognized effects in reducing the inflammatory response to colonizing bacteria in the premature intestine. We have discovered that toll like receptor 4 (TLR4) activation on the intestinal epithelium plays a critical role in NEC development, as mice lacking TLR4 on the intestinal epithelium are protected from NEC. We also determined that TLR4 expression on the intestinal epithelium is higher in the premature human and mouse intestine, which in mice reflects a novel role played by TLR4 in the regulation of intestinal differentiation. Importantly, the factors responsible for the elevated TLR4 signaling, and mechanisms capable of restraining TLR4 in the premature intestine, remain largely unknown. We now show that AHR expression is low in mouse and human NEC where TLR4 is high, and that activation of AHR within the newborn intestinal mucosa by dietary ligands, including those present in breast milk, restrain TLR4 signaling and attenuate NEC. Further, the administration of AHR ligands to the pregnant mother prevents NEC in the offspring. Importantly, we have identified novel AHR ligands that can prevent NEC in mice through reduced TLR4 signaling, and which reduce inflammation in human NEC tissue ex vivo. We thus hypothesize that AHR in the newborn gut plays a previously unrecognized role in restraining the hyper-inflammatory response of the newborn intestinal mucosa to colonizing microbes by limiting TLR4 signaling in the intestinal epithelium, thus protecting against NEC, and further, that activation of AHR by dietary factors including those in breast milk, can restrain TLR4 signaling and prevent NEC. Further, we hypothesize that the administration of an AHR ligand to the pregnant mother can reduce NEC severity in the pup. Finally, we propose that a recently discovered AHR ligand in our lab, termed ?A18?, may represent a novel strategy for NEC prevention and treatment. We will test this hypothesis in 3 aims: Aim 1: To understand the role of the Aryl Hydrocarbon Receptor in the newborn intestinal epithelium in the pathogenesis and treatment of NEC; Aim 2 To determine the effects and mechanisms by which the administration of a diet rich in AHR ligands to the pregnant mother protects against NEC in the offspring. Aim 3. To evaluate the role of a recently discovered AHR agonist, A18, in the prevention and treatment of experimental NEC in mice and piglets. These studies will make a significant conceptual advance by defining how dietary ligands can activate AHR and reduce inflammation in the premature intestinal epithelium, and provide a novel approach for NEC prevention through intra-partum administration of novel AHR ligands.